Electrosurgical method and apparatus for removing tissue within a bone body

ABSTRACT

A method for treating a bone body comprises inserting a probe having at least one active electrode into the target tissue and applying a voltage difference between an active electrode and return electrode to ablate the tissue. The method is particularly directed to removing tumors in a bone body and or removing cancellous bone in a bone body. The bone body may be a vertebral body. An apparatus includes a plurality of active electrodes and a distal section including two bends. The bends serve to prevent the active electrodes from impinging upon the shaft of an introducer needle. Also, a kit includes an electrosurgical probe, an electrosurgical generator, an introducer needle, and a fluid connector to connect the introducer needle to a fluid source such that liquid may be supplied to the target site during an application.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 10/970,796filed Oct. 20, 2004, which claims priority to 60/512,954 filed Oct. 20,2003, both applications of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to treating diseased bone byremoving tissue from within the bone and more particularly, byimmediately removing neoplastic and osteoporotic tissue using aminimally invasive electrosurgical probe. The present invention isparticularly well suited for the treatment of the vertebrae as well asother bone bodies such as, for example, the femur.

Vertebroplasty is a minimally invasive percutaneous approach to treatvertebral compression fractures (VCFs). VCFs may be secondary toosteoporosis or to the presence of (and treatment) of a tumor in thevertebrae (e.g., myelomas or metastatic tumors).

Vertebroplasty involves injecting a viscous solution of bone cement(e.g., poly-methylmethacrylate) into the fractured vertebral body. Thecement fills the spaces between the bone fragments and serves tostabilize the vertebral body, preventing spinal collapse. The viscoussolution may include a radio-opaque material to provide fluoroscopicguidance for the physician. See, for example, U.S. Pat. Nos. 6,348,055and 6,138,190 both issued to Preissman, describing a system for deliveryof implant material to a desired site. Each patent and patentapplication mentioned in this patent application is hereby incorporatedby reference in its entirety.

A problem with vertebroplasty procedures is the small space availablewithin the vertebral body that may be filled with the bone cement. Smallspaces in the vertebral body are generally undesirable because only asmall volume of stabilizing bone cement may be added to the space. Incontrast, a large space may accept a large amount of bone cement,tending to increase the life of the semi-artificial bone body.

Another problem with vertebroplasty is providing a solid surface for thebone cement to adhere. Providing a solid smooth surface for the cementto adhere to is not trivial because osteoporotic bone often consists ofa multitude of bone fragments in a haphazard arrangement. Accordingly, alarger smoother cavity is desirable in vertebroplasty.

A number of patents discuss creating a space or cavity in the vertebralbody for certain diagnostic and therapeutic procedures such as aprocedure for fixing a bone fracture. U.S. Pat. No. 4,969,888 issued toScholten et al. describes a method for fixation of osteoporotic bonecomprising drilling the osteoporotic bone to form a cavity, followed byinflating an inflatable device inserted into the cavity. Expansion ofthe inflatable device compacts the bone and is stated to restore thebone height. A flowable synthetic bone material is directed into thecavity and allowed to set to a hardened condition.

U.S. Pat. No. 6,440,138 issued to Reiley (the “Reiley patent”) describesanother device and method for creating cavities in an interior bodyregion such as cancellous bone. According to the Reiley patent, varioustools carry structures that cut cancellous bone to form the cavity. Thecutting structures include filaments in the form of a loop, or brush, ablade that may be moved laterally or rotatetively or both. Also, thestructure may comprise a transmitter of energy. The Reiley patent atcolumn 8, lines 19-30, indicates that the type of energy that thetransmitter propagates to remove tissue can vary. Described examplesinclude ultrasonic energy and laser energy at a suitable tissue cuttingfrequency.

A number of patents describe instruments and methods for treating tumorsby applying energy from a radio frequency source. See, for example, U.S.Pat. No. 6,622,731 to Daniel.

Although the above described techniques are available, each techniquehas associated shortcomings. For instance, drilling and compacting theosteoporotic bone fails to remove the bone fragments. The compactedfragments provide an unstable surface for the bone cement to adhere to.The bone fragments may be reabsorbed by the bone body, leaving a voidwhich may facilitate spinal collapse.

Additionally, inserting, expanding and deflating an inflatable memberrequires additional time and steps. A balloon also does not removetissue. It compacts the tissue, leaving dead tissue within the bonebody. The eventual reabsorbing of tissue leaves a void in the bone bodyand consequently, the patient may continue to be vulnerable to spinalcollapse.

Treating tumors with heat generated from RF energy can also fail toimmediately remove the tissue. As the necrotic tissue is reabsorbed, avoid develops in the bone body. Such voids lead to spinal collapse.

Accordingly, a fast minimally invasive procedure and apparatus fortreating bone disease of an osteoportic and non-osteoporotic origin isstill desired.

SUMMARY OF THE INVENTION

The present invention is a method for removing a volume of tissue withina bone body comprising: a.) inserting a distal end of an apparatus intothe bone body, the apparatus comprising an elongate shaft and an activeelectrode at or near the distal end, the active electrode being inelectrical communication with a radio frequency controller or currentgenerator; and b.) applying a radio frequency voltage or current to theactive electrode sufficient to cause the volume to be immediatelyremoved whereby a cavity is formed within the bone body.

The apparatus may comprise at least two active electrodes. In onevariation, at least one active electrode is a ball wire. The shape ofthe active electrode may include an equatorial cusp and an apical spike.Each of the at least two active electrodes is connected to a wireconductor that extends at least partially through the shaft. The wireconductors collectively form a wire bundle.

The apparatus may further comprise a securing member that is wrappedaround the wire bundle to prevent the active electrodes from radiallyexpanding. The apparatus may further comprise a polymeric tubularelement that holds the active electrodes in close proximity to oneanother. The tubular element may be positioned interior to the securingmember. The apparatus may also comprise a distal portion having S-curveor bend.

The method may be carried out to operate on a bone body such as avertebral body. The volume of tissue to be removed may be cancellousbone, a tumor, or another type of tissue.

The method may also comprise the step of injecting a stabilizingmaterial (such as bone cement) into the cavity.

The method may also comprise supplying a venous coagulant solution priorto the step of injecting. An example of a coagulant is THROMBIN-JMI®.Coagulation may then be confirmed by injecting a saline with a tracerand observing lack of venous uptake.

The method may further comprise delivering an electrically conductivefluid to the active electrode. Additionally, during the step of applyinga radio frequency current in step b.), described above, a plasma may beformed around the active electrode, the plasma having sufficient energyto molecularly disassociate the tissue.

Another variation of the present invention is an apparatus for removingtissue within a bone body comprising an elongate shaft having a distalend; at least two active electrodes arranged at or near the distal end;a wire bundle having at least two wire conductors, the wire conductorsextending at least partially through the shaft and connected to the atleast two active electrodes in a one to one correspondence; a returnelectrode spaced proximal to the active electrodes; and a malleablemember wrapped around a distal section of the wire bundle to prevent theactive electrodes from spreading apart from one another in anapplication.

The malleable member may comprise a metal wire. The apparatus mayfurther comprise a polymeric tubular member arranged concentrically withthe wire bundle, the polymeric tubular member being between the wirebundle and the malleable member. The apparatus may also comprise atleast two bends, each bend being between 5 and 30 degrees. Also, each ofthe active electrodes may have a cusp and an apical tip. In oneembodiment, the active electrodes form a bouquet arrangement.

In another variation the probe is connected to a fluid connector and thefluid connector comprises a fluid ingress port configured to fluidlycommunicate with an electrically conductive fluid source, and a fluidegress port configured to fluidly communicate with an introducer needleassembly. The fluid connector is also adapted to axially slide along theshaft.

Another variation of the present invention is a method for treatingabnormal bone comprising instantaneously creating a cavity in the boneby ablating a volume of tissue using a radio frequency energy source.The abnormal bone may be fractured, osteoporotic, neoplastic, tissue ofnonosteoporotic origin, or a combination of the tissues. The step ofusing radio frequency energy may comprise creating a plasma to cause thevolume of the bone tissue to be removed. The method may also comprisesupplying an electrically conductive fluid to a target site. The methodmay be carried out such that the tissue is molecularly disassociated.

Another variation of the present invention is a kit comprising: anintroducer needle for penetrating a vertebrae; an apparatus as recitedabove; a high frequency generator in electrical communication with theapparatus. The kit may further comprise a fluid valve adapted to coupleto a fluid source and to a proximal end of the introducer needle, andthe valve further being slideable along the shaft.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H illustrate steps of a spinal surgical procedure inaccordance with the present invention.

FIG. 2A is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis;

FIG. 2B schematically illustrates one embodiment of a power supplyaccording to the present invention;

FIG. 3 illustrates an electrosurgical system incorporating a pluralityof active electrodes and associated current limiting elements;

FIG. 4 is a side view of an electrosurgical probe;

FIG. 5 is a view of the distal end portion of the probe of FIG. 4;

FIG. 6 is an exploded view of a proximal portion of an electrosurgicalprobe;

FIGS. 7A-7D illustrate four embodiments of electrosurgical probesdesigned for treating spinal defects;

FIG. 8 illustrates an electrosurgical system incorporating a dispersivereturn pad for monopolar and/or bipolar operations;

FIG. 9 is a side view of an electrosurgical probe;

FIG. 10 is a side view of the distal end portion of the electrosurgicalprobe of FIG. 9;

FIG. 11 is a side view of an electrosurgical probe having a curvedshaft;

FIG. 12 is a side view of the distal end portion of the curved shaft ofFIG. 11, with the shaft distal end portion within an introducer device;

FIG. 13 is a side view of the distal end portion of an electrosurgicalprobe showing an active electrode having an apical spike and anequatorial cusp;

FIG. 14 is a cross-sectional view of the distal end portion of theelectrosurgical probe of FIG. 13;

FIG. 15 is a side view of the distal end portion a shaft of anelectrosurgical probe, indicating the position of a first curve and asecond curve in relation to the head of the active electrode;

FIG. 16A shows the distal end portion of the shaft of an electrosurgicalprobe extended distally from an introducer needle;

FIG. 16B illustrates the position of the active electrode in relation tothe inner wall of the introducer needle upon retraction of the activeelectrode within the introducer needle;

FIG. 17A shows a probe having a curved distal end and a plurality ofactive electrodes arranged in a bouquet;

FIG. 17B shows an enlarged view of the distal end section of the probeshown in FIG. 17A;

FIG. 17C shows a partial cross section of a distal section of the probeshown in FIG. 17B;

FIG. 18A shows a probe assembly in an expanded view including a probe, afluid connector, and an introducer needle;

FIG. 18B shows the probe assembly of FIG. 18A assembled;

FIG. 19A, 19B show a side view and an end view, respectively, of acurved shaft of an electrosurgical probe, in relation to an introducerneedle;

FIG. 20 shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a plurality of depthmarkings;

FIG. 21 shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a mechanical stop;

FIG. 22 illustrates stages in manufacture of an active electrode of anelectrosurgical probe;

FIG. 23 schematically represents a series of steps involved in a methodof making a probe shaft;

FIG. 24 schematically represents a series of steps involved in a methodof making an electrosurgical probe;

FIG. 25 shows a probe with a marker; and

FIGS. 26-27 show a probe that may flex.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including tissue within a bone body such as tumors(especially metastatic tumors), osteoporotic bone fragments, and bonefragments of nonosteoporotic origin. Examples of procedures include, butare not limited to, any procedure that may benefit from creating a voidor cavity in a bone body such as a vertebroplasty procedure, channelingbone tissue, removing tumors, removing cancellous bone (in the spine,leg bones or other peripheral or non-peripheral bones), interspinoustissue, degenerative discs, laminectomy/discectomy procedures fortreating herniated discs, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, localized tears or fissures in theannulus, nucleotomy, disc fusion procedures, medial facetectomy,posterior lumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar discectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy, orpercutaneous and the like.

A method for removing a bone tumor is described in FIGS. 1A to 1H.Referring first to FIG. 1A, a portion of the spine is shown. Inparticular, three vertebral bodies are shown. In an application, thediseased vertebral body 1 is identified and an introducer needle 2having an obturator is inserted into the vertebral body.

The introducer needle 2 may be a metallic needle having a hollow shaft.It may have a diameter from 0.5 to 5 mm, or perhaps up to 10 mm. Itslength may vary. Its length may range from 3 to 8 inches, and perhaps upto 15 inches, depending on the type of procedure. For example, thelength will vary depending on the level to be treated and the size ofthe patient.

A sharp or pointed obturator is provided to prevent tissue from fillingthe introducer needle as well as facilitate penetration through the hardcortical bone. The obturator may comprise a radiopaque material or itmay be made of a plastic. The obturator may be rigid and it may havevarious tip configurations to facilitate penetration of different typesof tissue.

As shown in FIG. 1B, the introducer needle is extended through thepedicle, the cortical bone tissue, the cancellous bone tissue 3, andultimately into or near the tumor 4 to be removed.

FIG. 1C shows the introducer needle touching the tumor with theobturator removed.

FIG. 1D shows insertion of an electrosurgical probe 5, described morefully in connection with FIG. 2A et seq. Also, another probe suitablefor use with this method is described in co pending patent applicationU.S. patent application Ser. No. 10/613,115, filed Jul. 3, 2003,incorporated by reference herein in its entirety.

The probe 5 is configured to apply energy to ablate tissue within a bonebody, creating a void or space 6. In particular, the probe 5 contains atleast one active electrode that is connected to a radiofrequency source.Application of a voltage difference between the active electrode and areturn electrode disintegrates the tumor tissue into harmlesscomponents, leaving a space 6. Unlike other technologies using radiofrequency energy, however, the present invention does not leave thetissue in place to be absorbed by the bone body over time in a sloweventual manner. Instead, the present invention ablates the tissue suchthat the tissue is immediately removed. As will be discussed in moredetail below, and while not being bound to theory, the mechanism ofaction of the present invention is related to formation of a plasma atthe probe tip.

FIG. 1E shows the tumor removed leaving a large open space 6. Once thetumor is removed, it is desirable to stabilize the vertebral body. Anopen space, crack, fragment, etc. can facilitate spinal collapseresulting in serious pain, if not dehabilitation.

Accordingly, a vertebroplasty may desirably be performed as shown inFIG. 1F. In particular, a flowable bone cement 7 is injected into thespace 6. A suitable cement injection system may include a connector thatcooperates with the introducer needle 2. An example of a cement deliverysystem is EZFLOW™ CEMENT DELIVERY SYSTEM, manufactured by ParallaxMedical Inc., Scotts Valley Calif.

FIG. 1G indicates the space 6 filled with bone cement 7. Overtime, thebone cement will harden forming a solidified mass as shown in FIG. 1H.In some cases, the bone cement may permeate the rest of the vertebralbody. Examples of bone cement are PMMA type acrylic resins such asSECOUR™, manufactured by Parallax Medical Inc., Scotts Valley, Calif.However, a wide variety of stabilizing material may be used to fill thespace, 6 some of which having radio pacifiers to increase visualizationof the flow. Specific aspects of the apparatus, system, and kits forperforming various procedures to remove tissue within a bone body aredescribed in more detail below.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconductive fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a liquid or gas,such as isotonic saline, blood, extracelluar or intracellular fluid,delivered to, or already present at, the target site, or a viscousfluid, such as a gel, applied to the target site. Since the vapor layeror vaporized region has a relatively high electrical impedance, itminimizes the current flow into the electrically conductive fluid. Thisionization, under the conditions described herein, induces the dischargeof energetic electrons and photons from the vapor layer and to thesurface of the target tissue. A more detailed description of thisphenomena, termed Coblation® can be found in commonly assigned U.S. Pat.No. 5,697,882 the complete disclosure of which is incorporated herein byreference.

Applicant believes that the principle mechanism of tissue removal in theCoblation® mechanism of the present invention is energetic electrons orions that have been energized in a plasma adjacent to the activeelectrode(s). When a liquid is heated enough that atoms vaporize off thesurface faster than they recondense, a gas is formed. When the gas isheated enough that the atoms collide with each other and knock theirelectrons off in the process, an ionized gas or plasma is formed (theso-called “fourth state of matter”). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995), the complete disclosure of which is incorporated herein byreference. When the density of the vapor layer (or within a bubbleformed in the electrically conducting liquid) becomes sufficiently low(i.e., less than approximately 10²⁰ atoms/cm³ for aqueous solutions),the electron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

Plasmas may be formed by heating a gas and ionizing the gas by drivingan electric current through it, or by shining radio waves into the gas.Generally, these methods of plasma formation give energy to freeelectrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

In one method of the present invention, one or more active electrodesare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the active electrodes and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below.

In addition to the above, applicant has discovered that the Coblation®mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the active electrode(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of active electrodes;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 eV to 5 eV to break(typically on the order of about 8 eV). Accordingly, the presentinvention in its current configuration generally does not ablate orremove such fatty tissue. However, the present invention may be used toeffectively ablate cells to release the inner fat content in a liquidform. Of course, factors may be changed such that these double bonds canalso be broken in a similar fashion as the single bonds (e.g.,increasing voltage or changing the electrode configuration to increasethe current density at the electrode tips). A more complete descriptionof this phenomena can be found in U.S. Pat. No. 6,355,032, filed Feb.27, 1998, the complete disclosure of which is incorporated herein byreference.

In yet other embodiments, the present invention provides systems,apparatus and methods for selectively removing tumors, e.g., spinaltumors, facial tumors, or other undesirable body structures whileminimizing the spread of viable cells from the tumor. Conventionaltechniques for removing such tumors generally result in the productionof smoke in the surgical setting, termed an electrosurgical or laserplume, which can spread intact, viable bacterial or viral particles fromthe tumor or lesion to the surgical team or to other portions of thepatient's body. This potential spread of viable cells or particles hasresulted in increased concerns over the proliferation of certaindebilitating and fatal diseases, such as hepatitis, herpes, HIV andpapillomavirus. In the present invention, high frequency voltage isapplied between the active electrode(s) and one or more returnelectrode(s) to volumetrically remove at least a portion of the tissuecells in the tumor through the dissociation or disintegration of organicmolecules into non-viable atoms and molecules. The present invention mayprovide an immediate removal of tissue. Specifically, the presentinvention converts the solid tissue cells into non-condensable gasesthat are no longer intact or viable, and thus, not capable of spreadingviable tumor particles to other portions of the patient's bone, vesselor brain or to the surgical staff The high frequency voltage ispreferably selected to effect controlled removal of these tissue cellswhile minimizing substantial tissue necrosis to surrounding orunderlying tissue. A more complete description of this phenomena can befound in U.S. patent application Ser. No. 09/109,219, filed Jun. 30,1998, the complete disclosure of which is incorporated herein byreference.

The electrosurgical probe or catheter of the present invention cancomprise a shaft or a handpiece having a proximal end and a distal endwhich supports one or more active electrode(s). The shaft or handpiecemay assume a wide variety of configurations, with the primary purposebeing to mechanically support the active electrode and permit thetreating physician to manipulate the electrode from a proximal end ofthe shaft. The shaft may be rigid or flexible, with flexible shaftsoptionally being combined with a generally rigid external tube formechanical support. Flexible shafts may be combined with pull wires,shape memory actuators, and other known mechanisms for effectingselective deflection of the distal end of the shaft to facilitatepositioning of the electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

The electrosurgical instrument may also be a catheter that is deliveredpercutaneously and/or endoluminally into the patient by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode or electrode arrayintegral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

The active electrode(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in and around the spinal cord, however, makes a bipolardesign more preferable because this minimizes the current flow throughnon-target tissue and surrounding nerves. Accordingly, the returnelectrode is preferably either integrated with the instrument body, oranother instrument located in close proximity thereto. The proximal endof the instrument(s) will include the appropriate electrical connectionsfor coupling the return electrode(s) and the active electrode(s) to ahigh frequency power supply, such as an electrosurgical generator.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a pHless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode. A more detailed description of such electrodeconfigurations can be found in U.S. Pat. No. 5,843,019, the completedisclosure of which is incorporated herein by reference.

The return electrode is typically spaced proximally from the activeelectrode(s) a suitable distance to avoid electrical shorting betweenthe active and return electrodes in the presence of electricallyconductive fluid. In most of the embodiments described herein, thedistal edge of the exposed surface of the return electrode is spacedabout 0.5 mm to 25 mm from the proximal edge of the exposed surface ofthe active electrode(s), preferably about 1.0 mm to 5.0 mm. Of course,this distance may vary with different voltage ranges, conductive fluids,and depending on the proximity of tissue structures to active and returnelectrodes. The return electrode will typically have an exposed lengthin the range of about 1 mm to 20 mm.

The current flow path between the active electrodes and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductivefluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conductive fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood or extracellular saline, may besufficient to establish a conductive path between the returnelectrode(s) and the active electrode(s), and to provide the conditionsfor establishing a vapor layer, as described above. However, conductivefluid that is introduced into the patient is generally preferred overblood because blood will tend to coagulate at certain temperatures. Inaddition, the patient's blood may not have sufficient electricalconductivity to adequately form a plasma in some applications.Advantageously, a liquid electrically conductive fluid (e.g., isotonicsaline) may be used to concurrently “bathe” the target tissue surface toprovide an additional means for removing any tissue, and to cool theregion of the target tissue ablated in the previous moment.

The power supply, or generator, may include a fluid interlock forinterrupting power to the active electrode(s) when there is insufficientconductive fluid around the active electrode(s). This ensures that theinstrument will not be activated when conductive fluid is not present,minimizing the tissue damage that may otherwise occur. A more completedescription of such a fluid interlock can be found in commonly assigned,U.S. Pat. No. 6,235,020, filed Apr. 10, 1998, the complete disclosure ofwhich is incorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensable gaseousproducts of ablation. In addition, it may be desirable to aspirate smallpieces of tissue or other body structures that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention may include one ormore suction lumen(s) in the instrument, or on another instrument,coupled to a suitable vacuum source for aspirating fluids from thetarget site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation active electrode(s), orthe same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, U.S. Pat. No. 6,190,381, filed Jan. 21,1998, the complete disclosure of which is incorporated herein byreference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath, or thelike. This embodiment has the advantage of ensuring that the conductivefluid, tissue fragments or ablation products do not flow through thepatient's vasculature or into other portions of the body. In addition,it may be desirable to limit the amount of suction to limit theundesirable effect suction may have on hemostasis of severed bloodvessels.

Apparatuses may use a single active electrode or an array of activeelectrodes spaced around the distal surface of a catheter or probe. Inthe latter embodiment, the electrode array usually includes a pluralityof independently current-limited and/or power-controlled activeelectrodes to apply electrical energy selectively to the target tissuewhile limiting the unwanted application of electrical energy to thesurrounding tissue and environment resulting from power dissipation intosurrounding electrically conductive fluids, such as blood, normalsaline, and the like. The active electrodes may be independentlycurrent-limited by isolating the terminals from each other andconnecting each terminal to a separate power source that is isolatedfrom the other active electrodes. Alternatively, the active electrodesmay be connected to each other at either the proximal or distal ends ofthe catheter to form a single wire that couples to a power source.

In one configuration, each individual active electrode in the electrodearray is electrically insulated from all other active electrodes in thearray within the instrument and is connected to a power source which isisolated from each of the other active electrodes in the array or tocircuitry which limits or interrupts current flow to the activeelectrode when low resistivity material (e.g., blood, electricallyconductive saline irrigant or electrically conductive gel) causes alower impedance path between the return electrode and the individualactive electrode. The isolated power sources for each individual activeelectrode may be separate power supply circuits having internalimpedance characteristics which limit power to the associated activeelectrode when a low impedance return path is encountered. By way ofexample, the isolated power source may be a user selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the instrument, connectors, cable, controller, or alongthe conductive path from the controller to the distal tip of theinstrument. Alternatively, the resistance and/or capacitance may occuron the surface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

The tip region of the instrument may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conductive fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the active electrodes with conductionof high frequency current from each individual active electrode to thereturn electrode. The current flow from each individual active electrodeto the return electrode(s) is controlled by either active or passivemeans, or a combination thereof, to deliver electrical energy to thesurrounding conductive fluid while minimizing energy delivery tosurrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalsaffects shrinking, cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. In some embodiments of thepresent invention, the tissue volume over which energy is dissipated(i.e., a high current density exists) may be more precisely controlled,for example, by the use of a multiplicity of small active electrodeswhose effective diameters or principal dimensions range from about 10 mmto 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferablyfrom about 1 mm to 0.1 mm. In this embodiment, electrode areas for bothcircular and non-circular terminals will have a contact area (per activeelectrode) below 50 mm² for electrode arrays and as large as 75 mm² forsingle electrode embodiments. In multiple electrode array embodiments,the contact area of each active electrode is typically in the range from0.0001 mm² to 1 mm², and more preferably from 0.001 mm² to 0.5 mm². Thecircumscribed area of the electrode array or active electrode is in therange from 0.25 mm² to 75 mm², preferably from 0.5 mm² to 40 mm². Inmultiple electrode embodiments, the array will usually include at leasttwo isolated active electrodes, often at least five active electrodes,often greater than 10 active electrodes and even 50 or more activeelectrodes, disposed over the distal contact surfaces on the shaft. Theuse of small diameter active electrodes increases the electric fieldintensity and reduces the extent or depth of tissue heating as aconsequence of the divergence of current flux lines which emanate fromthe exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or active electrode(s)will be formed at the distal tip of the electrosurgical instrumentshaft, frequently being planar, disk-shaped, or hemispherical surfacesfor use in reshaping procedures or being linear arrays for use incutting. Alternatively or additionally, the active electrode(s) may beformed on lateral surfaces of the electrosurgical instrument shaft(e.g., in the manner of a spatula), facilitating access to certain bodystructures in endoscopic procedures.

It should be clearly understood that the invention is not limited toelectrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the catheter shaft to apower source of high frequency current. Alternatively, the instrumentmay incorporate a single electrode that extends directly through thecatheter shaft or is connected to a single lead that extends to thepower source. The active electrode(s) may have ball shapes (e.g., fortissue vaporization and desiccation), twizzle shapes (for vaporizationand needle-like cutting), spring shapes (for rapid tissue debulking anddesiccation), twisted metal shapes, annular or solid tube shapes or thelike. Alternatively, the electrode(s) may comprise a plurality offilaments, rigid or flexible brush electrode(s) (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), side-effectbrush electrode(s) on a lateral surface of the shaft, coiledelectrode(s) or the like.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the active electrode(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between the activeelectrode(s) and the tissue at the treatment site throughout theprocedure, which reduces the thermal damage that might otherwise occurif the vapor layer were extinguished due to a lack of conductive fluid.Provision of the electrically conductive fluid around the target sitealso helps to maintain the tissue temperature at desired levels.

In other embodiments, the active electrodes are spaced from the tissue asufficient distance to minimize or avoid contact between the tissue andthe vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

The electrically conductive fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe active electrode(s). The electrical conductivity of the fluid (inunits of millisiemens per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

The voltage difference applied between the return electrode(s) and theactive electrode(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, often lessthan 350 kHz, and often between about 100 kHz and 200 kHz. In someapplications, applicant has found that a frequency of about 100 kHz isuseful because the tissue impedance is much greater at this frequency.In other applications, such as procedures in or around the heart or headand neck, higher frequencies may be desirable (e.g., 400-600 kHz) tominimize low frequency current flow into the heart or the nerves of thehead and neck. The RMS (root mean square) voltage applied will usuallybe in the range from about 5 volts to 1000 volts, preferably being inthe range from about 10 volts to 500 volts, often between about 150volts to 400 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation, cutting orablation). Typically, the peak-to-peak voltage for ablation or cuttingwith a square wave form will be in the range of 10 volts to 2000 voltsand preferably in the range of 100 volts to 1800 volts and morepreferably in the range of about 300 volts to 1500 volts, often in therange of about 300 volts to 800 volts peak to peak (again, depending onthe electrode size, number of electrons, the operating frequency and theoperation mode). Lower peak-to-peak voltages will be used for tissuecoagulation, thermal heating of tissue, or collagen contraction and willtypically be in the range from 50 to 1500, preferably 100 to 1000 andmore preferably 120 to 400 volts peak-to-peak (again, these values arecomputed using a square wave form). Higher peak-to-peak voltages, e.g.,greater than about 800 volts peak-to-peak, may be desirable for ablationof harder material, such as bone, depending on other factors, such asthe electrode geometries and the composition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being treated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular spinal surgery, neurosurgery procedure, cardiac surgery,arthroscopic surgery, dermatological procedure, ophthalmic procedures,open surgery or other endoscopic surgery procedure. For cardiacprocedures and potentially for neurosurgery, the power source may havean additional filter, for filtering leakage voltages at frequenciesbelow 100 kHz, particularly voltages around 60 kHz. Alternatively, apower source having a higher operating frequency, e.g., 300 kHz to 600kHz may be used in certain procedures in which stray low frequencycurrents may be problematic. A description of one suitable power sourcecan be found in commonly assigned U.S. Pat. Nos. 6,142,992 and6,235,020, both of which were filed Apr. 10, 1998, the completedisclosures of both applications are incorporated herein by referencefor all purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent active electrode, where the inductance of the inductoris in the range of 10 uH to 50,000 uH, depending on the electricalproperties of the target tissue, the desired tissue heating rate and theoperating frequency. Alternatively, capacitor-inductor (LC) circuitstructures may be employed, as described previously in U.S. Pat. No.5,697,909, the complete disclosure of which is incorporated herein byreference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual active electrode in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from the active electrode into the low resistance medium (e.g.,saline irrigant or blood).

Referring to FIG. 2A, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site, and a fluid source 21 for supplyingelectrically conductive fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site. The endoscope maybe integral with probe 10, or it may be part of a separate instrument.The system 11 may also include a vacuum source (not shown) for couplingto a suction lumen or tube 211 (see FIG. 4) in the probe 10 foraspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each ofelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site. Fluid supply tube 15 may be connected to a suitablepump (not shown), if desired.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to active electrodes 58. In anexemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “sub-ablation” mode (e.g., for coagulation orcontraction of tissue). The third foot pedal 39 allows the user toadjust the voltage level within the “ablation” mode. In the ablationmode, a sufficient voltage is applied to the active electrodes toestablish the requisite conditions for molecular dissociation of thetissue (i.e., vaporizing a portion of the electrically conductive fluid,ionizing charged particles within the vapor layer and accelerating thesecharged particles against the tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the subablation mode, the power supply 28 applies a low enoughvoltage to the active electrodes to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and sub-ablation modes by alternately stepping onfoot pedals 37, 38, respectively. In some embodiments, this allows thesurgeon to quickly move between coagulation/thermal heating and ablationin situ, without having to remove his/her concentration from thesurgical field or without having to request an assistant to switch thepower supply. By way of example, as the surgeon is sculpting tissue inthe ablation mode, the probe typically will simultaneously seal and/orcoagulation small severed vessels within the tissue. However, largervessels, or vessels with high fluid pressures (e.g., arterial vessels)may not be sealed in the ablation mode. Accordingly, the surgeon cansimply step on foot pedal 38, automatically lowering the voltage levelbelow the threshold level for ablation, and apply sufficient pressureonto the severed vessel for a sufficient period of time to seal and/orcoagulate the vessel. After this is completed, the surgeon may quicklymove back into the ablation mode by stepping on foot pedal 37.

Referring now to FIGS. 2B and 3, a representative high frequency powersupply for use according to the principles of the present invention willnow be described. The high frequency power supply of the presentinvention is configured to apply a high frequency voltage of about 10volts RMS to 500 volts RMS between one or more active electrodes (and/orcoagulation electrode) and one or more return electrodes. In theexemplary embodiment, the power supply applies about 70 volts RMS to 350volts RMS in the ablation mode and about 20 volts to 90 volts in asubablation mode, preferably 45 volts to 70 volts in the subablationmode (these values will, of course, vary depending on the probeconfiguration attached to the power supply and the desired mode ofoperation).

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being treated, and/or the maximum allowedtemperature selected for the probe tip. The power supply allows the userto select the voltage level according to the specific requirements of aparticular procedure, e.g., spinal surgery, arthroscopic surgery,dermatological procedure, ophthalmic procedures, open surgery, or otherendoscopic surgery procedure.

As shown in FIG. 2B, the power supply generally comprises a radiofrequency (RF) power oscillator 70 having output connections forcoupling via a power output signal 71 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300 kHz to 600 kHz. In particular,for cardiac applications, the RF oscillator will preferably operate inthe range of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 71 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to the activeelectrodes and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

Power is supplied to RF oscillator 70 by a switching power supply 72coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 72 allows powersupply 28 to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 72 operates at about100 kHz.

A controller 74 coupled to the operator controls 73 (i.e., foot pedalsand voltage selector) and display 76, is connected to a control input ofthe switching power supply 72 for adjusting the generator output powerby supply voltage variation. The controller 74 may be a microprocessoror an integrated circuit. The power supply may also include one or morecurrent sensors 75 for detecting the output current. The power supply ispreferably housed within a metal casing which provides a durableenclosure for the electrical components therein. In addition, the metalcasing reduces the electromagnetic noise generated within the powersupply because the grounded metal casing functions as a “Faradayshield,” thereby shielding the environment from internal sources ofelectromagnetic noise.

The power supply generally comprises a main or mother board containinggeneric electrical components required for many different surgicalprocedures (e.g., arthroscopy, urology, general surgery, dermatology,neurosurgery, etc.), and a daughter board containing applicationspecific current-limiting circuitry (e.g., inductors, resistors,capacitors and the like). The daughter board is coupled to the motherboard by a detachable multi-pin connector to allow convenient conversionof the power supply to, e.g., applications requiring a different currentlimiting circuit design. For arthroscopy, for example, the daughterboard preferably comprises a plurality of inductors of about 200 to 400microhenries, usually about 300 microhenries, for each of the channelssupplying current to the active electrodes 102 (see FIG. 4).

Alternatively, in one embodiment, current limiting inductors are placedin series with each independent active electrode, where the inductanceof the inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending International Application No. PCT/US94/05168, the completedisclosure of which is incorporated herein by reference. Additionally,current limiting resistors may be selected. Preferably, these resistorswill have a large positive temperature coefficient of resistance sothat, as the current level begins to rise for any individual activeelectrode in contact with a low resistance medium (e.g., saline irrigantor conductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from theactive electrode into the low resistance medium (e.g., saline irrigantor conductive gel). Power output signal may also be coupled to aplurality of current limiting elements 96, which are preferably locatedon the daughter board since the current limiting elements may varydepending on the application. A more complete description of arepresentative power supply can be found in commonly assigned U.S. Pat.No. 6,142,992, previously incorporated herein by reference.

FIGS. 4-6 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.4, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises an electrically conducting material,usually metal, which is selected from the group comprising tungsten,stainless steel alloys, platinum or its alloys, titanium or its alloys,molybdenum or its alloys, and nickel or its alloys. In this embodiment,shaft 100 includes an electrically insulating jacket 108, which istypically formed as one or more electrically insulating sheaths orcoatings, such as polytetrafluoroethylene, polyimide, and the like. Theprovision of the electrically insulating jacket over the shaft preventsdirect electrical contact between these metal elements and any adjacentbody structure or the surgeon. Such direct electrical contact between abody structure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis. Alternatively, the return electrode may comprise anannular band coupled to an insulating shaft and having a connectorextending within the shaft to its proximal end.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 6), and provides a suitable interface for connection to anelectrical connecting cable distal portion 22 (see FIG. 2A) Electrodesupport member 102 extends from the distal end of shaft 100 (usuallyabout 1 mm to 20 mm), and provides support for a plurality ofelectrically isolated active electrodes 104 (see FIG. 5). As shown inFIG. 4, a fluid tube 233 extends through an opening in handle 204, andincludes a connector 235 for connection to a fluid supply source, forsupplying electrically conductive fluid to the target site. Depending onthe configuration of the distal surface of shaft 100, fluid tube 233 mayextend through a single lumen (not shown) in shaft 100, or it may becoupled to a plurality of lumens (also not shown) that extend throughshaft 100 to a plurality of openings at its distal end. In therepresentative embodiment, tubing 239 is a tube that extends along theexterior of shaft 100 to a point just distal of return electrode 112(see FIG. 5). In this embodiment, the fluid is directed through anopening 237 past return electrode 112 to the active electrodes 104.Probe 20 may also include a valve 17 (FIG. 2A) or equivalent structurefor controlling the flow rate of the electrically conductive fluid tothe target site.

As shown in FIG. 4, the distal portion of shaft 100 is preferably bentto improve access to the operative site of the tissue being treated.Electrode support member 102 has a substantially planar tissue treatmentsurface 212 (FIG. 5) that is usually at an angle of about 10 degrees to90 degrees relative to the longitudinal axis of shaft 100, preferablyabout 30 degrees to 60 degrees and more preferably about 45 degrees. Inalternative embodiments, the distal portion of shaft 100 comprises aflexible material which can be deflected relative to the longitudinalaxis of the shaft. Such deflection may be selectively induced bymechanical tension of a pull wire, for example, or by a shape memorywire that expands or contracts by externally applied temperaturechanges. A more complete description of this embodiment can be found inU.S. Pat. No. 5,697,909, the complete disclosure of which has previouslybeen incorporated herein by reference. Alternatively, the shaft 100 ofthe present invention may be bent by the physician to the appropriateangle using a conventional bending tool or the like.

In the embodiment shown in FIGS. 4 to 6, probe 20 includes a returnelectrode 112 for completing the current path between active electrodes104 and a high frequency power supply 28 (see FIG. 2A). As shown, returnelectrode 112 preferably comprises an exposed portion of shaft 100shaped as an annular conductive band near the distal end of shaft 100slightly proximal to tissue treatment surface 212 of electrode supportmember 102, typically about 0.5 mm to 10 mm and more preferably about 1mm to 10 mm. Return electrode 112 or shaft 100 is coupled to a connector258 that extends to the proximal end of probe 10/20, where it issuitably connected to power supply 28 (FIG. 2A).

As shown in FIG. 4, return electrode 112 is not directly connected toactive electrodes 104. To complete this current path so that activeelectrodes 104 are electrically connected to return electrode 112, anelectrically conductive fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconductive fluid is delivered through fluid tube 233 to opening 237, asdescribed above. Alternatively, the conductive fluid may be delivered bya fluid delivery element (not shown) that is separate from probe 20. Inarthroscopic surgery, for example, the target area of the joint will beflooded with isotonic saline and the probe 90 will be introduced intothis flooded target area. Electrically conductive fluid can becontinually resupplied to maintain the conduction path between returnelectrode 112 and active electrodes 104. In other embodiments, thedistal portion of probe 20 may be dipped into a source of electricallyconductive fluid, such as a gel or isotonic saline, prior to positioningat the target site. Applicant has found that the surface tension of thefluid and/or the viscous nature of a gel allows the conductive fluid toremain around the active and return electrodes for long enough tocomplete its function according to the present invention, as describedbelow. Alternatively, the conductive fluid, such as a gel, may beapplied directly to the target site.

In alternative embodiments, the fluid path may be formed in probe 90 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIGS. 8Aand 8B). This annular gap may be formed near the perimeter of the shaft100 such that the electrically conductive fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in U.S. Pat. No.5,697,281, the complete disclosure of which has previously beenincorporated herein by reference.

Referring to FIG. 5, the electrically isolated active electrodes 104 arespaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range of1 mm to 20 mm. The individual active electrodes 104 preferably extendoutward from tissue treatment surface 212 by a distance of about 0.1 mmto 4 mm, usually about 0.2 mm to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around active electrodes 104 to facilitatethe ablation and shrinkage of tissue as described in detail above.

In the embodiment of FIGS. 4 to 6, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3-15) around the perimeterof surface 212 (see FIG. 5). Alternatively, the probe may include asingle, annular, or partially annular, active electrode at the perimeterof the tissue treatment surface. The central opening 209 is coupled to asuction lumen (not shown) within shaft 100 and a suction tube 211 (FIG.4) for aspirating tissue, fluids and/or gases from the target site. Inthis embodiment, the electrically conductive fluid generally flowsradially inward past active electrodes 104 and then back through theopening 209. Aspirating the electrically conductive fluid during surgeryallows the surgeon to see the target site, and it prevents the fluidfrom flowing into the patient's body.

Of course, it will be recognized that the distal tip of anelectrosurgical probe of the invention, e.g. probe 10/20/90, may have avariety of different configurations. For example, the probe may includea plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (see FIG. 7B). In this embodiment, the activeelectrodes 104 extend distally from the center of tissue treatmentsurface 212 such that they are located radially inward from openings209. The openings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and suction tube 211for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

FIG. 6 illustrates the electrical connections 250 within handle 204 forcoupling active electrodes 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple active electrodes 104 to a plurality of pins 254, which areplugged into a connector block 256 for coupling to a connecting cabledistal end 22 (FIG. 2A). Similarly, return electrode 112 is coupled toconnector block 256 via a wire 258 and a plug 260.

According to the present invention, the probe 20 further includes anidentification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe (e.g., 20) includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.In some embodiments, the voltage reduction element allows the powersupply 28 to apply two different voltages simultaneously to twodifferent electrodes (see FIG. 7D). In other embodiments, the voltagereduction element primarily allows the electrosurgical probe to becompatible with various electrosurgical generators supplied byArthroCare Corporation (Sunnyvale, Calif.) that are adapted to applyhigher voltages for ablation or vaporization of tissue. For thermalheating or coagulation of tissue, for example, the voltage reductionelement will serve to reduce a voltage of about 100 volts rms to 170volts rms (which is a setting of 1 or 2 on the ArthroCare Model 970 and980 (i.e., 2000) Generators) to about 45 volts rms to 60 volts rms,which is a suitable voltage for coagulation of tissue without ablation(e.g., molecular dissociation) of the tissue.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, the cable 34 and/or cable distal end 22 that couples thepower supply 28 to the probe may be used as a voltage reduction element.The cable has an inherent capacitance that can be used to reduce thepower supply voltage if the cable is placed into the electrical circuitbetween the power supply, the active electrodes and the returnelectrode. In this embodiment, the cable distal end 22 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor. Further, it should be noted that thepresent invention can be used with a power supply that is adapted toapply a voltage within the selected range for treatment of tissue. Inthis embodiment, a voltage reduction element or circuitry may not bedesired.

FIGS. 7A to 7D illustrate embodiments of an electrosurgical probe 350specifically designed for the treatment of herniated or diseased spinaldiscs. Referring to FIG. 7A, probe 350 comprises an electricallyconductive shaft 352, a handle 354 coupled to the proximal end of shaft352 and an electrically insulating support member 356 at the distal endof shaft 352. Probe 350 further includes a shrink wrapped insulatingsleeve 358 over shaft 352, and an exposed portion of shaft 352 thatfunctions as the return electrode 360. In the representative embodiment,probe 350 comprises a plurality of active electrodes 362 extending fromthe distal end of support member 356. As shown, return electrode 360 isspaced a further distance from active electrodes 362 than in theembodiments described above. In this embodiment, the return electrode360 is spaced a distance of about 2.0 mm to 50 mm, preferably about 5 mmto 25 mm from active electrodes 362. In addition, return electrode 360has a larger exposed surface area than in previous embodiments, having alength in the range of about 2.0 mm to 40 mm, preferably about 5 mm to20 mm. Accordingly, electric current passing from active electrodes 362to return electrode 360 will follow a current flow path 370 that isfurther away from shaft 352 than in the previous embodiments. In someapplications, this current flow path 370 results in a deeper currentpenetration into the surrounding tissue with the same voltage level, andthus increased thermal heating of the tissue. As discussed above, thisincreased thermal heating may have advantages in some applications oftreating disc or other spinal abnormalities. Typically, it is desired toachieve a tissue temperature in the range of about 60° C. to 100° C. toa depth of about 0.2 mm to 5 mm, usually about 1 mm to 2 mm. The voltagerequired for this thermal damage will partly depend on the electrodeconfigurations, the conductivity of the tissue and the area immediatelysurrounding the electrodes, the time period in which the voltage isapplied and the depth of tissue damage desired. With the electrodeconfigurations described in FIGS. 7A-7D, the voltage level for thermalheating will usually be in the range of about 20 volts rms to 300 voltsrms, preferably about 60 volts rms to 200 volts rms. The peak-to-peakvoltages for thermal heating with a square wave form having a crestfactor of about 2 are typically in the range of about 40 to 600 voltspeak-to-peak, preferably about 120 to 400 volts peak-to-peak. The higherthe voltage is within this range, the less time required. If the voltageis too high, however, the surface tissue may be vaporized, debulked orablated, which is undesirable.

In alternative embodiments, the electrosurgical system used inconjunction with probe 350 may include a dispersive return electrode 450(see FIG. 8) for switching between bipolar and monopolar modes. In thisembodiment, the system will switch between an ablation mode, where thedispersive pad 450 is deactivated and voltage is applied between activeand return electrodes 362, 360, and a subablation or thermal heatingmode, where the active electrode(s) 362 are deactivated and voltage isapplied between the dispersive pad 450 and the return electrode 360. Inthe subablation mode, a lower voltage is typically applied and thereturn electrode 360 functions as the active electrode to providethermal heating and/or coagulation of tissue surrounding returnelectrode 360.

FIG. 7B illustrates yet another probe. As shown, electrosurgical probe350 comprises an electrode assembly 372 having one or more activeelectrode(s) 362 and a proximally spaced return electrode 360 as inprevious embodiments. Return electrode 360 is typically spaced about 0.5mm to 25 mm, preferably 1.0 mm to 5.0 mm from the active electrode(s)362, and has an exposed length of about 1 mm to 20 mm. In addition,electrode assembly 372 includes two additional electrodes 374, 376spaced axially on either side of return electrode 360. Electrodes 374,376 are typically spaced about 0.5 mm to 25 mm, preferably about 1 mm to5 mm from return electrode 360. In the representative embodiment, theadditional electrodes 374, 376 are exposed portions of shaft 352, andthe return electrode 360 is electrically insulated from shaft 352 suchthat a voltage difference may be applied between electrodes 374, 376 andelectrode 360. In this embodiment, probe 350 may be used in at least twodifferent modes, an ablation mode and a subablation or thermal heatingmode. In the ablation mode, voltage is applied between activeelectrode(s) 362 and return electrode 360 in the presence ofelectrically conductive fluid, as described above. In the ablation mode,electrodes 374, 376 are deactivated. In the thermal heating orcoagulation mode, active electrode(s) 362 are deactivated and a voltagedifference is applied between electrodes 374, 376 and electrode 360 suchthat a high frequency current 370 flows therebetween, as shown in FIG.7B. In the thermal heating mode, a lower voltage is typically appliedbelow the threshold for plasma formation and ablation, but sufficient tocause some thermal damage to the tissue immediately surrounding theelectrodes without vaporizing or otherwise debulking this tissue so thatthe current 370 provides thermal heating and/or coagulation of tissuesurrounding electrodes 360, 372, 374.

FIG. 7C illustrates another probe 350 incorporating an electrodeassembly 372 having one or more active electrode(s) 362 and a proximallyspaced return electrode 360 as in previous embodiments. Return electrode360 is typically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0mm from the active electrode(s) 362, and has an exposed length of about1 mm to 20 mm. In addition, electrode assembly 372 includes a secondactive electrode 380 separated from return electrode 360 by anelectrically insulating spacer 382. In this embodiment, handle 354includes a switch 384 for toggling probe 350 between at least twodifferent modes, an ablation mode and a subablation or thermal heatingmode. In the ablation mode, voltage is applied between activeelectrode(s) 362 and return electrode 360 in the presence ofelectrically conductive fluid, as described above. In the ablation mode,electrode 380 is deactivated. In the thermal heating or coagulationmode, active electrode(s) 362 may be deactivated and a voltagedifference is applied between electrode 380 and electrode 360 such thata high frequency current 370 flows therebetween. Alternatively, activeelectrode(s) 362 may not be deactivated as the higher resistance of thesmaller electrodes may automatically send the electric current toelectrode 380 without having to physically decouple electrode(s) 362from the circuit. In the thermal heating mode, a lower voltage istypically applied below the threshold for plasma formation and ablation,but sufficient to cause some thermal damage to the tissue immediatelysurrounding the electrodes without vaporizing or otherwise debulkingthis tissue so that the current 370 provides thermal heating and/orcoagulation of tissue surrounding electrodes 360, 380.

Of course, it will be recognized that a variety of other embodiments maybe used to accomplish similar functions as the embodiments describedabove. For example, electrosurgical probe 350 may include a plurality ofhelical bands formed around shaft 352, with one or more of the helicalbands having an electrode coupled to the portion of the band such thatone or more electrodes are formed on shaft 352 spaced axially from eachother.

FIG. 7D illustrates another probe designed for channeling through tissueand creating lesions. This probe may be useful in a wide variety ofapplications such as, for example, treatment of spinal discs and/orsnoring and sleep apnea. As shown, probe 350 is similar to the probe inFIG. 7C having a return electrode 360 and a third, coagulation electrode380 spaced proximally from the return electrode 360. In this embodiment,active electrode 362 comprises a single electrode wire extendingdistally from insulating support member 356. Of course, the activeelectrode 362 may have a variety of configurations to increase thecurrent densities on its surfaces, e.g., a conical shape tapering to adistal point, a hollow cylinder, loop electrode and the like. In therepresentative embodiment, support members 356 and 382 are constructedof a material, such as ceramic, glass, silicone and the like. Theproximal support member 382 may also comprise a more conventionalorganic material as this support member 382 will generally not be in thepresence of a plasma that would otherwise etch or wear away an organicmaterial.

The probe 350 in FIG. 7D does not include a switching element. In thisembodiment, all three electrodes are activated when the power supply isactivated. The return electrode 360 has an opposite polarity from theactive and coagulation electrodes 362, 380 such that current 370 flowsfrom the latter electrodes to the return electrode 360 as shown. In thepreferred embodiment, the electrosurgical system includes a voltagereduction element or a voltage reduction circuit for reducing thevoltage applied between the coagulation electrode 380 and returnelectrode 360. The voltage reduction element allows the power supply 28to, in effect, apply two different voltages simultaneously to twodifferent electrodes. Thus, for channeling through tissue, the operatormay apply a voltage sufficient to provide ablation of the tissue at thetip of the probe (i.e., tissue adjacent to the active electrode 362). Atthe same time, the voltage applied to the coagulation electrode 380 willbe insufficient to ablate tissue. For thermal heating or coagulation oftissue, for example, the voltage reduction element will serve to reducea voltage of about 100 volts rms to 300 volts rms to about 45 volts rmsto 90 volts rms, which is a suitable voltage for coagulation of tissuewithout ablation (e.g., molecular dissociation) of the tissue.

In the representative embodiment, the voltage reduction elementcomprises a pair of capacitors forming a bridge divider (not shown)coupled to the power supply and coagulation electrode 380. Thecapacitors usually have a capacitance of about 200 pF to 500 pF (at 500volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course,the capacitors may be located in other places within the system, such asin, or distributed along the length of, the cable, the generator, theconnector, etc. In addition, it will be recognized that other voltagereduction elements, such as diodes, transistors, inductors, resistors,capacitors or combinations thereof, may be used in conjunction with thepresent invention. For example, the probe 350 may include a codedresistor (not shown) that is constructed to lower the voltage appliedbetween the return and coagulation electrodes 360, 380, respectively. Inaddition, electrical circuits may be employed for this purpose.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, cable 22/34 that couples power supply 28 to the probe 90may be used as a voltage reduction element. The cable has an inherentcapacitance that can be used to reduce the power supply voltage if thecable is placed into the electrical circuit between the power supply,the active electrodes and the return electrode. In this embodiment,cable 22/34 may be used alone, or in combination with one of the voltagereduction elements discussed above, e.g., a capacitor. Further, itshould be noted that the present invention can be used with a powersupply that is adapted to apply two different voltages within theselected range for treatment of tissue. In this embodiment, a voltagereduction element or circuitry may not be desired.

In one specific embodiment, the probe 350 is manufactured by firstinserting an electrode wire (active electrode 362) through a ceramictube (insulating member 356) such that a distal portion of the wireextends through the distal portion of the tube, and bonding the wire tothe tube, typically with an appropriate epoxy. A stainless steel tube(return electrode 360) is then placed over the proximal portion of theceramic tube, and a wire (e.g., nickel wire) is bonded, typically byspot welding, to the inside surface of the stainless steel tube. Thestainless steel tube is coupled to the ceramic tube by epoxy, and thedevice is cured in an oven or other suitable heat source. A secondceramic tube (insulating member 382) is then placed inside of theproximal portion of the stainless steel tube, and bonded in a similarmanner. The shaft 358 is then bonded to the proximal portion of thesecond ceramic tube, and an insulating sleeve (e.g. polyimide) iswrapped around shaft 358 such that only a distal portion of the shaft isexposed (i.e., coagulation electrode 380). The nickel wire connectionwill extend through the center of shaft 358 to connect return electrode360 to the power supply. The active electrode 362 may form a distalportion of shaft 358, or it may also have a connector extending throughshaft 358 to the power supply.

In use, the physician positions active electrode 362 adjacent to thetissue surface to be treated (e.g., a spinal disc). The power supply isactivated to provide an ablation voltage between active and returnelectrodes 362, 360, respectively, and a coagulation or thermal heatingvoltage between coagulation and return electrodes 380, 360,respectively. An electrically conductive fluid can then be providedaround active electrode 362, and in the junction between the active andreturn electrodes 360, 362 to provide a current flow path therebetween.This may be accomplished in a variety of manners, as discussed above.The active electrode 362 is then advanced through the space left by theablated tissue to form a channel in the disc. During ablation, theelectric current between the coagulation and return electrode istypically insufficient to cause any damage to the surface of the tissueas these electrodes pass through the tissue surface into the channelcreated by active electrode 362. Once the physician has formed thechannel to the appropriate depth, he or she will cease advancement ofthe active electrode, and will either hold the instrument in place forapproximately 5 seconds to 30 seconds, or can immediately remove thedistal tip of the instrument from the channel (see detailed discussionof this below). In either event, when the active electrode is no longeradvancing, it will eventually stop ablating tissue.

Prior to entering the channel formed by the active electrode 362, anopen circuit exists between return and coagulation electrodes 360, 380.Once coagulation electrode 380 enters this channel, electric currentwill flow from coagulation electrode 380, through the tissue surroundingthe channel, to return electrode 360. This electric current will heatthe tissue immediately surrounding the channel to coagulate any severedvessels at the surface of the channel. If the physician desires, theinstrument may be held within the channel for a period of time to createa lesion around the channel, as discussed in more detail below.

FIG. 8 illustrates yet another embodiment of an electrosurgical system440 incorporating a dispersive return pad 450 attached to theelectrosurgical probe 400. In this embodiment, the invention functionsin the bipolar mode as described above. In addition, the system 440 mayfunction in a monopolar mode in which a high frequency voltagedifference is applied between the active electrode(s) 410, and thedispersive return pad 450. In the exemplary embodiment, the pad 450 andthe probe 400 are coupled together, and are both disposable, single-useitems. The pad 450 includes an electrical connector 452 that extendsinto handle 404 of probe 400 for direct connection to the power supply.Of course, the invention would also be operable with a standard returnpad that connects directly to the power supply. In this embodiment, thepower supply 460 will include a switch, e.g., a foot pedal 462, forswitching between the monopolar and bipolar modes. In the bipolar mode,the return path on the power supply is coupled to return electrode 408on probe 400, as described above. In the monopolar mode, the return pathon the power supply is coupled to connector 452 of pad 450, activeelectrode(s) 410 are decoupled from the electrical circuit, and returnelectrode 408 functions as the active electrode. This allows the surgeonto switch between bipolar and monopolar modes during, or prior to, thesurgical procedure. In some cases, it may be desirable to operate in themonopolar mode to provide deeper current penetration and, thus, agreater thermal heating of the tissue surrounding the return electrodes.In other cases, such as ablation of tissue, the bipolar modality may bepreferable to limit the current penetration to the tissue.

In one configuration, the dispersive return pad 450 is adapted forcoupling to an external surface of the patient in a region substantiallyclose to the target region. For example, during the treatment of tissuein the head and neck, the dispersive return pad is designed andconstructed for placement in or around the patient's shoulder, upperback or upper chest region. This design limits the current path throughthe patient's body to the head and neck area, which minimizes the damagethat may be generated by unwanted current paths in the patient's body,particularly by limiting current flow through the patient's heart. Thereturn pad is also designed to minimize the current densities at thepad, to thereby minimize patient skin burns in the region where the padis attached.

FIG. 9 is a side view of an electrosurgical probe 900, according to oneembodiment of the invention. Probe 900 includes a shaft 902 having adistal end portion 902 a and a proximal end portion 902 b. An activeelectrode 910 is disposed on distal end portion 902 a. Although only oneactive electrode is shown in FIG. 9, embodiments including a pluralityof active electrodes are also within the scope of the invention. Probe900 further includes a handle 904 which houses a connection block 906for coupling electrodes, e.g. active electrode 910, thereto. Connectionblock 906 includes a plurality of pins 908 adapted for coupling probe900 to a power supply unit, e.g. power supply 28 (FIG. 2A).

FIG. 10 is a side view of the distal end portion of the electrosurgicalprobe of FIG. 9, showing details of shaft distal end portion 902 a.Distal end portion 902 a includes an insulating collar or spacer 916proximal to active electrode 910, and a return electrode 918 proximal tocollar 916. A first insulating sleeve (FIG. 14) may be located beneathreturn electrode 918. A second insulating jacket or sleeve 920 mayextend proximally from return electrode 918. Second insulating sleeve920 serves as an electrical insulator to inhibit current flow into theadjacent tissue. In a currently preferred embodiment, probe 900 furtherincludes a shield 922 extending proximally from second insulating sleeve920. Shield 922 may be formed from a conductive metal such as stainlesssteel, and the like. Shield 922 functions to decrease the amount ofleakage current passing from probe 900 to a patient or a user (e.g.,surgeon). In particular, shield 922 decreases the amount of capacitivecoupling between return electrode 918 and an introducer needle 928 (FIG.19A). Typically shield 922 is coupled to an outer floating conductivelayer or cable shield (not shown) of a cable, e.g. cables 22, 34 (FIG.2A), connecting probe 900 to power supply 28. In this way, the capacitorbalance of shaft 902 is disturbed. In one embodiment, shield 922 may becoated with a durable, hard compound such as titanium nitride. Such acoating has the advantage of providing reduced friction between shield922 and introducer inner wall 932 as shaft 902 is axially translatedwithin introducer needle 928 (e.g., FIGS. 19A, 19B).

FIG. 11 is a side view of an electrosurgical probe 900 showing a firstcurve 924 and a second curve 926 located at distal end portion 902 a,wherein second curve 926 is proximal to first curve 924. First curve 924and second curve 926 may be separated by a linear (i.e. straight, ornon-curved), or substantially linear, inter-curve portion 925 of shaft902.

FIG. 12 is a side view of shaft distal end portion 902 a within arepresentative introducer device or needle 928 having an inner diameterD. Shaft distal end portion 902 a includes first curve 924 and secondcurve 926 separated by inter-curve portion 925. In one embodiment, shaftdistal end portion 902 a includes a linear or substantially linearproximal portion 901 extending from proximal end portion 902 b to secondcurve 926, a linear or substantially linear inter-curve portion 925between first and second curves 924, 926, and a linear or substantiallylinear distal portion 909 between first curve 924 and the distal tip ofshaft 902 (the distal tip is represented in FIG. 12 as an electrode head911). When shaft distal end portion 902 a is located within introducerneedle 928, first curve 924 subtends a first angle ∀ to the innersurface of needle 928, and second curve 926 subtends a second angle ∃ toinner surface 932 of needle 928. (In the situation shown in FIG. 12,needle inner surface 932 is essentially parallel to the longitudinalaxis of shaft proximal end portion 902 b (FIG. 11).) In one embodiment,shaft distal end portion 902 a is designed such that the shaft distaltip occupies a substantially central transverse location within thelumen of introducer needle 928 when shaft distal end portion 902 a istranslated axially with respect to introducer needle 928. Thus, as shaftdistal end portion 902 a is advanced through the distal opening ofneedle 928 (FIGS. 16B, 19A), and then retracted back into the distalopening, the shaft distal tip will always occupy a transverse locationtowards the center of introducer needle 928 (even though the tip may becurved or biased away from the longitudinal axis of shaft 902 and needle928 upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion 902 a is flexible andhas a configuration which requires shaft distal end portion 902 a bedistorted in the region of at least second curve 926 by application of alateral force imposed by inner wall 932 of introducer needle 928 asshaft distal end portion 902 a is introduced or refracted into needle928. In one embodiment, first curve 924 and second curve 926 are in thesame plane relative to the longitudinal axis of shaft 902, and first andsecond curves 924, 926 are in opposite directions.

The “S-curve” configuration of shaft 902 shown in FIGS. 11-C allows thedistal end or tip of a device to be advanced or retracted through needledistal end 928 a and within the lumen of needle 928 without the distalend or tip contacting introducer needle 928. Accordingly, this designallows a sensitive or delicate component to be located at the distal tipof a device, wherein the distal end or tip is advanced or retractedthrough a lumen of an introducer instrument comprising a relatively hardmaterial (e.g., an introducer needle comprising stainless steel). Thisdesign also allows a component located at a distal end or tip of adevice to be constructed from a relatively soft material, and for thecomponent located at the distal end or tip to be passed through anintroducer instrument comprising a hard material without risking damageto the component comprising a relatively soft material.

The “S-curve” design of shaft distal end portion 902 a allows the distaltip (e.g., electrode head 911) to be advanced and retracted through thedistal opening of needle 928 while avoiding contact between the distaltip and the edges of the distal opening of needle 928. (If, for example,shaft distal end portion 902 a included only a single curve the distaltip would ordinarily come into contact with needle distal end 928 a asshaft 902 is retracted into the lumen of needle 928.) In preferredembodiments, the length L2 of distal portion 909 and the angle ∀ betweendistal portion 909 and needle inner surface 932 928, when shaft distalend portion 902 a is compressed within needle 928, are selected suchthat the distal tip is substantially in the center of the lumen ofneedle 928, as shown in FIG. 12. Thus, as the length L2 increases, theangle ∀ will decrease, and vice versa. The exact values of length L2 andangle ∀ will depend on the inner diameter, D of needle 928, the innerdiameter, d of shaft distal end portion 902 a, and the size of the shaftdistal tip.

The presence of first and second curves, 924, 926 provides a pre-definedbias in shaft 902. In addition, in one embodiment shaft distal endportion 902 a is designed such that at least one of first and secondcurves 924, 926 are compressed to some extent as shaft distal endportion 902 a is retracted into the lumen of needle 928. Accordingly,the angle of at least one of curves 924, 926 may be changed when distalend portion 902 a is advanced out through the distal opening ofintroducer needle 928, as compared with the corresponding angle whenshaft distal end portion is completely retracted within introducerneedle 928. For example, FIG. 27C shows shaft 902 of FIG. 12 free fromintroducer needle 928, wherein first and second curves 924, 926 areallowed to adopt their natural or uncompressed angles ∀′ and ∃′,respectively, wherein ∃′ is typically equal to or greater than ∃. Angle∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ issubtended by inter-curve portion 925 and proximal portion 901. Whenshaft distal end portion 902 a is unrestrained by introducer needle 928,proximal portion 901 approximates the longitudinal axis of shaft 902.Angle ∀′ is subtended between linear distal portion 909 and a line drawnparallel to proximal portion 901. Electrode head 911 is omitted fromFIG. 27C for the sake of clarity.

The principle described above with reference to shaft 902 and introducerneedle 928 may equally apply to a range of other medical devices. Thatis to say, the “S-curve” configuration of the invention may be includedas a feature of any medical system or apparatus in which a medicalinstrument may be axially translated or passed within an introducerdevice. In particular, the principle of the “S-curve” configuration ofthe invention may be applied to any apparatus wherein it is desired thatthe distal end of the medical instrument does not contact or impingeupon the introducer device as the medical instrument is advanced from orretracted into the introducer device. The introducer device may be anyapparatus through which a medical instrument is passed. Such medicalsystems may include, for example, a catheter, a cannula, an endoscope,and the like.

When shaft 902 is advanced distally through the needle lumen to a pointwhere second curve 926 is located distal to needle distal end 928 a, theshaft distal tip is deflected from the longitudinal axis of needle 928.The amount of this deflection is determined by the relative size ofangles ∃′ and ∀′, and the relative lengths of L1 and L2. The amount ofthis deflection will in turn determine the size of a channel or lesion(depending on the application) formed in a tissue treated by electrodehead 911 when shaft 902 is rotated circumferentially with respect to thelongitudinal axis of probe 900.

As a result of the pre-defined bias in shaft 902, shaft distal endportion 902 a will contact a larger volume of tissue than a linear shafthaving the same dimensions. In addition, in one embodiment thepre-defined bias of shaft 902 allows the physician to guide or steer thedistal tip of shaft 902 by a combination of axial movement of needledistal end 928 a and the inherent curvature at shaft distal end portion902 a of probe 900.

Shaft 902 preferably has a length in the range of from about 4 to 30 cm.In one aspect of the invention, probe 900 is manufactured in a range ofsizes having different lengths and/or diameters of shaft 902. A shaft ofappropriate size can then be selected by the surgeon according to thebody structure or tissue to be treated and the age or size of thepatient. In this way, patients varying in size from small children tolarge adults can be accommodated. Similarly, for a patient of a givensize, a shaft of appropriate size can be selected by the surgeondepending on the organ or tissue to be treated, for example, whether anintervertebral disc to be treated is in the lumbar spine or the cervicalspine. For example, a shaft suitable for treatment of a disc of thecervical spine may be substantially smaller than a shaft for treatmentof a lumbar disc. For treatment of a lumbar disc in an adult, shaft 902is preferably in the range of from about 15 to 25 cm. For treatment of acervical disc, shaft 902 is preferably in the range of from about 4 toabout 15 cm.

The diameter of shaft 902 is preferably in the range of from about 0.5to about 2.5 mm, and more preferably from about 1 to 1.5 mm. First curve924 is characterized by a length L1, while second curve 926 ischaracterized by a length L2 (FIG. 12). Inter-curve portion 925 ischaracterized by a length L3, while shaft 902 extends distally fromfirst curve 924 a length L4. In one embodiment, L2 is greater than L1.Length L1 may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3 andL4 are each in the range of from about 1 to 6 mm.

FIG. 13 is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900 showing a head 911 of active electrode 910(the latter not shown in FIG. 13), according to one embodiment of theinvention. In this embodiment, electrode head 911 includes an apicalspike 911 a and an equatorial cusp 911 b. Electrode head 911 exhibits anumber of advantages as compared with, for example, an electrosurgicalprobe having a blunt, globular, or substantially spherical activeelectrode. In particular, electrode head 911 provides a high currentdensity at apical spike 911 a and cusp 911 b. In turn, high currentdensity in the vicinity of an active electrode is advantageous in thegeneration of a plasma; and, as is described fully hereinabove,generation of a plasma in the vicinity of an active electrode isfundamental to ablation of tissue with minimal collateral thermal damageaccording to certain embodiments of the instant invention. Electrodehead 911 provides an additional advantage, in that the sharp edges ofcusp 911 b, and more particularly of apical spike 911 a, facilitatemovement and guiding of head 911 into tissue during surgical procedures,as described fully hereinbelow. In contrast, an electrosurgical probehaving a blunt or rounded apical electrode is more likely to follow apath of least resistance, such as a channel which was previously ablatedwithin nucleus pulposus tissue. Although certain embodiments of theinvention depict head 911 as having a single apical spike, other shapesfor the apical portion of active electrode 910 are also within the scopeof the invention.

FIG. 14 is a longitudinal cross-sectional view of distal end portion 902a of shaft 902. Apical electrode head 911 is in communication with afilament 912. Filament 912 typically comprises an electricallyconductive wire encased within a first insulating sleeve 914. Firstinsulating sleeve 914 comprises an insulator, such as various syntheticpolymeric materials. An exemplary material from which first insulatingsleeve 914 may be constructed is a polyimide. First insulating sleeve914 may extend the entire length of shaft 902 proximal to head 911. Aninsulating collar or spacer 916 is disposed on the distal end of firstinsulating sleeve 914, adjacent to electrode head 911. Collar 916preferably comprises a material such as a glass, a ceramic, or silicone.The exposed portion of first insulating sleeve 914 (i.e., the portionproximal to collar 916) is encased within a cylindrical return electrode918. Return electrode 918 may extend proximally the entire length ofshaft 902. Return electrode 918 may comprise an electrically conductivematerial such as stainless steel, tungsten, platinum or its alloys,titanium or its alloys, molybdenum or its alloys, nickel or its alloys,and the like. A proximal portion of return electrode 918 is encasedwithin a second insulating sleeve 920, so as to provide an exposed bandof return electrode 918 located distal to second sleeve 920 and proximalto collar 916. Second sleeve 920 provides an insulated portion of shaft920 which facilitates handling of probe 900 by the surgeon during asurgical procedure. A proximal portion of second sleeve 920 is encasedwithin an electrically conductive shield 922. Second sleeve 920 andshield 922 may also extend proximally for the entire length of shaft902.

FIG. 15 is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900, indicating the position of first and secondcurves 924, 926, respectively. Probe 900 includes head 911, collar 916,return electrode 918, second insulating sleeve 920, and shield 922,generally as described with reference to FIGS. 13, 14. In the embodimentof FIG. 15, first curve 924 is located within return electrode 918,while second curve 926 is located within shield 922. However, accordingto various embodiments of the invention, shaft 902 may be provided inwhich one or more curves are present at alternative or additionallocations or components of shaft 902, other than the location of firstand second curves 924, 926, respectively, shown in FIG. 15.

FIG. 16A shows distal end portion 902 a of shaft 902 extended distallyfrom an introducer needle 928, according to one embodiment of theinvention. Introducer needle 928 may be used to conveniently introduceshaft 902 into tissue, such as the nucleus pulposus of an intervertebraldisc. In this embodiment, due to the curvature of shaft distal end 902a, when shaft 902 is extended distally beyond introducer needle 928,head 911 is displaced laterally from the longitudinal axis of introducerneedle 928. However, as shown in FIG. 16B, as shaft 902 is retractedinto introducer needle 928, head 911 assumes a substantially centraltransverse location within lumen 930 (see also FIG. 19B) of introducer928. Such re-alignment of head 911 with the longitudinal axis ofintroducer 928 is achieved by specific design of the curvature of shaftdistal end 902 a, as accomplished by the instant inventors. In thismanner, contact of various components of shaft distal end 902 a (e.g.,electrode head 911, collar 916, return electrode 918) is prevented,thereby not only facilitating extension and refraction of shaft 902within introducer 928, but also avoiding a potential source of damage tosensitive components of shaft 902.

FIGS. 17A-C show another electrosurgical probe 1200 that may perform aspinal surgery as well as other types of surgery. In particular, theprobe shown in FIGS. 17A-17C is intended for minimally invasivesurgeries that may require relatively large volumes or cavities to beformed in a bone body such as removal of a bone tumor in a vertebralbody.

Referring to FIG. 17A, the probe 1200 comprises a proximal end 1210 thatis adapted to connect with a cable, an elongate shaft 1220, and a curveddistal end 1230. The overall length of the probe may vary depending onthe application. An exemplary length for the shaft 1220 in a spinalsurgery procedure may be about 8-9 inches not including the proximal endconnector 1210. The probe diameter may range from 1 to 5 mm, and in onevariation ranges from 2 to 2.5 mm.

FIG. 17B shows an enlarged view of the distal end section of probe 1200of FIG. 17A. Distal end section 1230 includes a first bend 1232 and asecond bend 1234 forming an “s-curve” similar to that described in theabove mentioned probes. This type of bend tends to prevent the activeelectrodes 1240 a-c on the distal tip from contacting an introducerneedle (not shown) when the active electrodes exit the introducer needleand enter the target tissue. Similarly, when the active electrodes arewithdrawn into the introducer needle when the surgery is complete thes-curve tends to prevent the active electrode from contacting theintroducer needle. Contact between the introducer needle and the activeelectrodes can have detrimental effects on the ablation energy and isthus undesirable. The angle may vary and an exemplary angle is about 9degrees.

The distance from the second bend 1234 to the active electrode tip mayvary. An exemplary distance may range from 20 to 30 mm and perhaps about25 mm. Although the probe shown in FIG. 17A includes a particular bend,the invention is not intended to be so limited unless specificallyrecited so in the appended claims. Indeed, the probe may have no bend orother types of bends and curvatures.

The probe 1200 also includes a return electrode 1250 arranged proximalto the active electrodes on the shaft. The return electrode is coatedwith a polymeric coating 1251 proximally and includes a length ofexposed metal ranging from 0.5 to 10 mm and perhaps about 5 to 7 mm. Avoltage difference is applied between the active electrodes and thereturn electrode to ablate tissue during an application. In some cases,an electrolytically conductive fluid is delivered in the target area andcontacts the return and active electrodes. As described above, theelectrolytically conductive fluid is vaporized and a plasma is formedwhen a proper voltage differential is applied between the electrodes.The plasma-mediated ablation removes tissue quickly.

The active electrodes shown in FIG. 17B are arranged in a bouquet. Theactive electrodes thus spread to a degree when they are not confined byanother member such as an introducer needle. This arrangement allows alarger ablation channel to be formed during an application. More tissuemay be removed. The active electrodes may be shaped variously includinga shape as shown in FIG. 17B. The shape shown in FIG. 17B includes anequatorial cusp and an apical tip. The shape shown in FIG. 17B isbelieved to quickly remove tissue without causing necrosis of collateraltissue.

Each of the plurality of active electrodes are connected to a wireconductor that extends through the shaft. The wire conductorscollectively form a wire bundle and are joined to a cable (not shown)that connects the probe to an electrical source. Each of the wireconductors may be covered with a thin polymeric coating such aspolyimide.

FIG. 17C shows a partial cross section of a distal section of the probe1200. In particular, wire conductors 1238 a-c are shown forming a wirebundle. Additionally, an inner tubular non-electrically conductingmember 1254 is coaxially arranged on the exterior of the wire bundle toprovide an electrical gap between the active electrodes 1240 and thereturn electrode 1250. The tubular member may be, for example, asilicone tube. The silicone tube may extend a distance (d₁) from thedistal edge of the return electrode 1250. Distance d₁ may range from0.25 to 2 mm and more preferably from 0.75 to 1.25 mm and perhaps about1 mm. Also, the electrode heads may be spaced a distance (d₂) from thedistal edge of the silicone tube. Distance d₂ may range from 0.25 to 2.5mm and may be about 0.5 mm in one variation of the invention.

A securing member 1252 is arranged over the exterior of the siliconetube/wire bundle. An example of a securing member may be a metal wirethat is helically wrapped around the wire bundle to prevent the activeelectrodes from radially expanding more than a desired amount. The metalwire may be stainless steel, titanium, molybdenum, etc. The metal wiremay also have a polymeric coating such as polyimide. The thickness ofthe coating may vary and may be as small as about 15 microns. However,the polymeric coatings may have other thicknesses. Accordingly, theactive electrodes are prevented from radially expanding more than apredetermined amount in an application (such as when the probe isinserted into tissue and is no longer radially confined to the lumen ofan introducer needle). It is also to be understood, however, that asmall amount of radially expansion may be desirable to form a largerablation channel than the inner diameter of the lumen of the introducerneedle.

Additionally, a redundant member 1256 may be arranged over the helicallywrapped wire member. The redundant member may be, for example, heatshrink wrap tube and it may extend coaxially to cover the whole lengthof the inner silicone tube. An adhesive 1258 such as UV adhesive or asilicone adhesive may be added to bond all the components together.

FIGS. 18A-18B show an electrosurgical assembly or kit 1300 including anintroducer needle 1310, a fluid connector 1320, and an electrosurgicalprobe 1330 as described above in connection with FIGS. 17A-C.

The assembly may be used in a number of procedures such as theprocedures described above in connection with FIGS. 1A-1H.

FIG. 18A shows an exploded view illustrating how the components areinterconnected. In particular, the probe 1330 is inserted throughconnector 1320 and through needle 1310. The needle may be rigid and havea length suitable for the type of procedure.

The connector has an egress end 1322 that is configured to fluidlyconnect with a proximal end of the introducer needle. For example,connector and introducer needle may have Luer-type threads 1326. Theconnector further includes an ingress port 1324 for accepting fluid froma fluid source. A flexible tube 1340 may fluidly connect the fluidconnector to a stopcock 1342 that is configured to receive fluid fromthe fluid source. Indeed, a wide variety of fluid connector assembliesmay be employed to supply liquid to the introducer needle.

The introducer needle 1310 directs fluid to the target region where theactive electrodes of the probe are positioned. In this manner, theactive electrodes may operate in the presence of electrically conductivefluid. The probe tip may be urged distally and proximally relative tothe introducer needle. An example of a fluid connector 1320 is a maleTOUHY BORST with side port.

FIG. 18B shows the components described above in an assembled view.

FIG. 19A shows a side view of shaft 902 in relation to an inner wall 932of introducer needle 928 upon extension or retraction of electrode head911 from, or within, introducer needle 928. Shaft 902 is located withinintroducer 928 with head 911 adjacent to introducer distal end 928 a(FIG. 19B). Under these circumstances, curvature of shaft 902 may causeshaft distal end 902 a to be forced into contact with introducer innerwall 932, e.g., at a location of second curve 926. Nevertheless, due tothe overall curvature of shaft 902, and in particular the nature andposition of first curve 924 (FIGS. 11-B), head 911 does not contactintroducer distal end 928 a.

FIG. 19B shows an end view of electrode head 911 in relation tointroducer needle 928 at a point during extension or retraction of shaft902, wherein head 911 is adjacent to introducer distal end 928 a (FIGS.16B, 19B). In this situation, head 911 is substantially centrallypositioned within lumen 930 of introducer 928. Therefore, contactbetween head 911 and introducer 928 is avoided, allowing shaft distalend 902 a to be extended and retracted repeatedly without sustaining anydamage to shaft 902.

FIG. 20 shows shaft proximal end portion 902 b of electrosurgical probe900, wherein shaft 902 includes a plurality of depth markings 903 (shownas 903 a-f in FIG. 20). In other embodiments, other numbers andarrangements of depth markings 903 may be included on shaft 902. Forexample, in certain embodiments, depth markings may be present along theentire length of shield 922, or a single depth marking 903 may bepresent at shaft proximal end portion 902 b. Depth markings serve toindicate to the surgeon the depth of penetration of shaft 902 into apatient's tissue, organ, or body, during a surgical procedure. Depthmarkings 903 may be formed directly in or on shield 922, and maycomprise the same material as shield 922. Alternatively, depth markings903 may be formed from a material other than that of shield 922. Forexample, depth markings may be formed from materials which have adifferent color and/or a different level of radiopacity, as comparedwith material of shield 922. For example, depth markings may comprise ametal, such as tungsten, gold, or platinum oxide (black), having a levelof radiopacity different from that of shield 922. Such depth markingsmay be visualized by the surgeon during a procedure performed underfluoroscopy. In one embodiment, the length of the introducer needle andthe shaft 902 are selected to limit the range of the shaft beyond thedistal tip of the introducer needle.

FIG. 21 shows a probe 900, wherein shaft 902 includes a mechanical stop905. Preferably, mechanical stop 905 is located at shaft proximal endportion 902 b. Mechanical stop 905 limits the distance to which shaftdistal end 902 a can be advanced through introducer 928 by makingmechanical contact with a proximal end 928 b of introducer 928.Mechanical stop 905 may be a rigid material or structure affixed to, orintegral with, shaft 902. Mechanical stop 905 also serves to monitor thedepth or distance of advancement of shaft distal end 902 a throughintroducer 928, and the degree of penetration of distal end 902 a into apatient's tissue, organ, or body. In one embodiment, mechanical stop 905is movable on shaft 902, and stop 905 includes a stop adjustment unit907 for adjusting the position of stop 905 and for locking stop 905 at aselected location on shaft 902.

FIG. 22 illustrates stages in manufacture of an active electrode 910 ofa shaft 902, according to one embodiment of the present invention. Stage22-I shows an elongated piece of electrically conductive material 912′,e.g., a metal wire, as is well known in the art. Material 912′ includesa first end 912′a and a second end 912′b. Stage 22-II shows theformation of a globular structure 911′ from first end 912′a, whereinglobular structure 911′ is attached to filament 912. Globular structure911′ may be conveniently formed by applying heat to first end 912′a.Techniques for applying heat to the end of a metal wire are well knownin the art. Stage 22-III shows the formation of an electrode head 911from globular structure 911′, wherein active electrode 910 compriseshead 911 and filament 912 attached to head 911. In this particularembodiment, head 911 includes an apical spike 911 a and a substantiallyequatorial cusp 911 b.

FIG. 23 schematically represents a series of steps involved in a methodof making a shaft according to one embodiment of the present invention,wherein step 1000 involves providing an active electrode having afilament, the active electrode including an electrode head attached tothe filament. An exemplary active electrode to be provided in step 1000is an electrode of the type described with reference to FIG. 22. At thisstage (step 1000), the filament may be trimmed to an appropriate lengthfor subsequent coupling to a connection block (FIG. 9).

Step 1002 involves covering or encasing the filament with a firstinsulating sleeve of an electrically insulating material such as asynthetic polymer or plastic, e.g., a polyimide. Preferably, the firstinsulating sleeve extends the entire length of the shaft. Step 1004involves positioning a collar of an electrically insulating material onthe distal end of the first insulating sleeve, wherein the collar islocated adjacent to the electrode head. The collar is preferably amaterial such as a glass, a ceramic, or silicone. Step 1006 involvesplacing a cylindrical return electrode over the first insulating sleeve.Preferably, the return electrode is positioned such that its distal endis contiguous with the proximal end of the collar, and the returnelectrode preferably extends proximally for the entire length of theshaft. The return electrode may be constructed from stainless steel orother non-corrosive, electrically conductive metal.

According to one embodiment, a metal cylindrical return electrode ispre-bent to include a curve within its distal region (i.e. the returnelectrode component is bent prior to assembly onto the shaft). As aresult, the shaft assumes a first curve upon placing the returnelectrode over the first insulating sleeve, i.e. the first curve in theshaft results from the bend in the return electrode. Step 1008 involvescovering a portion of the return electrode with a second insulatinglayer or sleeve such that a band of the return electrode is exposeddistal to the distal end of the second insulating sleeve. In oneembodiment, the second insulating sleeve comprises a heat-shrink plasticmaterial which is heated prior to positioning the second insulatingsleeve over the return electrode. According to one embodiment, thesecond insulating sleeve is initially placed over the entire length ofthe shaft, and thereafter the distal end of the second insulating sleeveis cut back to expose an appropriate length of the return electrode.Step 1010 involves encasing a proximal portion of the second insulatingsleeve within a shield of electrically conductive material, such as acylinder of stainless steel or other metal, as previously describedherein.

FIG. 24 schematically represents a series of steps involved in a methodof making an electrosurgical probe of the present invention, whereinstep 1100 involves providing a shaft having at least one activeelectrode and at least one return electrode. An exemplary shaft to beprovided in step 1100 is that prepared according to the method describedhereinabove with reference to FIG. 23, i.e., the shaft includes a firstcurve. Step 1102 involves bending the shaft to form a second curve.Preferably, the second curve is located at the distal end portion of theshaft, but proximal to the first curve. In one embodiment, the secondcurve is greater than the first curve. (Features of both the first curveand second curve have been described hereinabove, e.g., with referenceto FIG. 12.) Step 1104 involves providing a handle for the probe. Thehandle includes a connection block for electrically coupling theelectrodes thereto. Step 1106 involves coupling the active and returnelectrodes of the shaft to the connection block. The connection blockallows for convenient coupling of the electrosurgical probe to a powersupply (e.g., power supply 28, FIG. 2A). Thereafter, step 1108 involvesaffixing the shaft to the handle.

FIG. 25 is a side view of an electrosurgical probe 900′ including shaft902″ having tracking device 942 located at distal end portion 902″a.Tracking device 942 may serve as a radiopaque marker adapted for guidingdistal end portion 902″a within a bone body or disc. Shaft 902″ alsoincludes at least one active electrode 910 disposed on the distal endportion 902″a. Preferably, electrically insulating support member orcollar 916 is positioned proximal of active electrode 910 to insulateactive electrode 910 from at least one return electrode 918. In mostembodiments, the return electrode 918 is positioned on the distal endportion of the shaft 902″ and proximal of the active electrode 910. Inother embodiments, however, return electrode 918 can be omitted fromshaft 902″, in which case at least one return electrode may be providedon ancillary device 940, or the return electrode may be positioned onthe patient's body, as a dispersive pad (not shown).

Although active electrode 910 is shown in FIG. 25 as comprising a singleapical electrode, other numbers, arrangements, and shapes for activeelectrode 910 are within the scope of the invention. For example, activeelectrode 910 can include a plurality of isolated electrodes in avariety of shapes. Active electrode 910 will usually have a smallerexposed surface area than return electrode 918, such that the currentdensity is much higher at active electrode 910 than at return electrode918. Preferably, return electrode 918 has a relatively large, smoothsurfaces extending around shaft 902″ in order to reduce currentdensities in the vicinity of return electrode 918, thereby minimizingdamage to non-target tissue.

While bipolar delivery of a high frequency energy is the preferredmethod of debulking the nucleus pulposus, it should be appreciated thatother energy sources (i.e., resistive, or the like) can be used, and theenergy can be delivered with other methods (i.e., monopolar, conductive,or the like) to debulk the nucleus.

FIG. 26 shows a steerable electrosurgical probe 950 including a shaft952, according to another embodiment of the invention. Preferably, shaft952 is flexible and may assume a substantially linear configuration asshown. Probe 950 includes handle 904, shaft distal end 952 a, activeelectrode 910, insulating collar 916, and return electrode 918. As canbe seen in FIG. 27, under certain circumstances, e.g., upon applicationof a force to shaft 952 during guiding or steering probe 950 during aprocedure, shaft distal end 952 a can adopt a non-linear configuration,designated 952′a. The deformable nature of shaft distal end 952′a allowsactive electrode 910 to be guided to a specific target site within abone body or disc.

Although the invention has been described primarily with respect toelectrosurgical treatment of the spine, it is to be understood that themethods and apparatus of the invention are also applicable to thetreatment of other tissues, organs, and bodily structures. For example,the principle of the “S-curve” configuration of the invention may beapplied to any medical system or apparatus in which a medical instrumentis passed within an introducer device, wherein it is desired that thedistal end of the medical instrument does not contact or impinge uponthe introducer device as the instrument is advanced from or retractedwithin the introducer device. The introducer device may be any apparatusthrough which a medical instrument is passed. Such a medical system orapparatus may include, for example, a catheter, a cannula, an endoscope,and the like. Thus, while the exemplary embodiments of the presentinvention have been described in detail, by way of example and forclarity of understanding, a variety of changes, adaptations, andmodifications will be obvious to those of skill in the art. Therefore,the scope of the present invention is limited solely by the appendedclaims.

1. An apparatus for removing tissue within a bone body comprising: anelongate shaft having a distal end; at least two active electrodesarranged at or near said distal end; a wire bundle having at least twowire conductors, said wire conductors extending at least partiallythrough said shaft and connected to said at least two active electrodesin a one to one correspondence; a return electrode spaced proximal tosaid active electrodes; and a malleable member wrapped around a distalsection of said wire bundle to prevent said active electrodes fromspreading apart from one another in an application.
 2. The apparatus ofclaim 1 wherein said malleable member comprises a metal wire.
 3. Theapparatus of claim 2 further comprising a polymeric tubular memberarranged concentrically with said wire bundle, said polymeric tubularmember being between said wire bundle and said malleable member.
 4. Theapparatus of claim 1 wherein said apparatus comprises at least twobends, each bend being between 5 and 30 degrees.
 5. The apparatus ofclaim 1 wherein each of said active electrodes has a cusp and an apicaltip.
 6. The apparatus of claim 5 wherein said active electrodes form abouquet arrangement.
 7. The apparatus of claim 1 further comprising afluid connector, said fluid connector comprising a fluid ingress portconfigured to fluidly communicate with a fluid source, and a fluidegress port configured to fluidly communicate with an introducer needleassembly, said fluid connector also adapted to axially slide along saidshaft.
 8. A kit comprising: an introducer needle for penetrating avertebrae; an apparatus as recited in claim 1; and a high frequencycontroller in electrical communication with said apparatus.
 9. The kitof claim 8 further comprising a fluid valve adapted to couple to a fluidsource and to a proximal end of said introducer needle, and said valvefurther being slideable along said shaft.
 10. The kit of claim 9 whereinsaid apparatus further comprises a suction lumen for aspiratingmaterials from the target site.